Rice, wheat, barley, corn, and such, which are important cereals worldwide, are crops whose seeds (embryo and endosperm) are used as food. Of such crops, barley has two-rowed and six-rowed varieties (FIG. 1). Barley forms three one-flowered spikelets per rachis; and barley varieties that have all three spikelets produce seeds are collectively called six-rowed barley, while varieties in which only the central spikelets produce seeds are generally called two-rowed barley. The difference between six-row and two-row types (hereinafter referred to as “row type”) directly influences the yield, because it has a great impact on determining the number, shape, and size of grains. The row type is also an important phenotype that affects the modes of use for barley, such as malt production, brewing, pearling, and feed. Furthermore, genetic studies have revealed that the row type is closely related to resistance to Fusarium head blight.
It has been revealed that the six-row type is a phenotype governed by a single recessive gene, vrs1, while Vrs1, the dominant gene for two-rowed barley, suppresses the development of lateral spikelets (FIG. 1). However, their gene products remain unknown. Furthermore, although the genomic structure (specifically, arrangement of homologous genes) is highly conserved among different cereal species, no genes homologous to the row-type gene are known. Even if such genes exist, their functions are unknown.
Prior art documents related to the present invention include:    Non-patent Document 1: Congfen He, et al. Genome 47:1122-1129 (2004)    Non-patent Document 2: Komatsuda T. and Tanno K. Comparative high resolution map of the six-rowed spike locus 1 (vrs1) in several populations of barley. Hordeum vulgare L. Hereditas 141:68-73 (2004)    Patent Document 1: Japanese Patent Application Kokai Publication No. (JP-A) 2004-313062 (unexamined, published Japanese patent application)